Effect of temperature, irradiation dose, and dose rate on the retention of some radioisotopes in poly(methyl methacrylate)/phosphate/composites

摘要

Polymer/composites have been prepared successfully consisting of natural phosphate powder and the monomer, N-methyl methacrylate, using gamma irradiation. The polymerization reaction was followed up using a thermogravimetric analyzer (TGA), and the region of the glass transition temperatures (T_g) of the samples was located using a thermomechanical analyzer (TMA) by applying the mode with alternative variable force; the mode with constant force was used to determine the T_g of the pure polymer and the polymer/composite prepared at the same irradiation dose. The effects of temperature, contact time, pH, dose, dose rate, monomer to phosphate ratio, and the concentration of concurrent element (Ca) on the migration of ~(137)Cs, ~(152)Eu and ~(52)Sr from a solid phase consisting of phosphate-poly(methyl methacrylate) composite to groundwater have been investigated. The ability of the produced composites to keep the studied radioisotopes in the solid phase is much higher than mineral phosphate at ambient temperatures. Element ratios of 100% in the solid phase can be achieved for Eu and Sr. Cesium ratio in the solid phase is higher than 95% (dose 15 kGy, dose rate 10.5 kCy/h). High irradiation doses (about 60 kGy) and dose rates (15 kGy/h) lead to quantitative retention of all studied elements in the solid phase, even in the presence of a concurrent element. This behavior can be explained by higher possibilities of crosslinking of the polymer chains due to higher doses and dose rates. High temperatures lead to lowering of retention ratios of the prepared composites.